Agricultural chemicals such as herbicides, pesticides, fertilizers, etc. are often applied to spraying processes from a vehicle such as a tractor which carries a tank of the liquid for distribution through a number of spray nozzles along a spray boom. Typical spray booms include nozzles directed to spray the liquid toward the ground surface. The nozzles are spaced elevationally from the ground surface by distances calculated to minimize wind drift of the spray droplets and to maximize the ground surface covered by the spray patterns. Nozzle size and operating pressures are factors determining the ground speed requirements for the associated vehicle. A common practice has been to use high pressure and low volume spray nozzles, with a number of the nozzles being used to increase the application rate and, hence, enable higher speeds for the associated tractor. Low volume, high pressure nozzles, however, easily clog and produce such fine droplets of spray that wind drift becomes a serious concern, especially with spot application of herbicide.
Another problem associated with sprayers is realized especially among orchardists who wish to apply herbicides in "kill strips" to opposite sides of tree rows. The sprayed material must be carefully applied to avoid contact with leaves of the orchard trees. Wind drift is therefore a very serious concern. Another concern is the amount of time required to apply the chemicals.
U.S. Pat. No. 4,586,287 to Bleasdale et al. discloses a spraying apparatus with special provisions for directing spray patterns to opposite sides of objects such as tree trunks. The device includes a spray boom that extends outwardly of a supporting vehicle. A rotatable spray head is situated at the boom end. The spray head includes a number of radially extending arms with a spray nozzle at the end of each. The arms are rotatable about a common vertical axis. Elements are included to enable the rotation of the arms responsive to engagement with a stationary object such as a tree trunk.